Circuit arrangement for igniting ignitrons



April 12, 1966 H. J. G. M. VAN DAELEN CIRCUIT ARRANGEMENT FOR IGNITING IGNITRONS Filed Jan. 11, 1962 2 Pk/OR ART FIGJ t 4001.15 IOU as T FIG-5 INVENTOR HENRI J.G.M.VAN DAE LEN BY v M?- AGENT United States Patent 3,246,203 CKRCUIT ARRANGEMENT FOR IGNITING IGNITRONS Henri Jean Gerard Marie van Daelen, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Deiaware Fited Jan. 11, 1962, Ser. No. 165,683 Claims priority, application Netherlands, Jan. 20, 1961,

Claims. (o1. 315-208 This invention relates. to I control circuits and, ,more particularly, to control circuits for controlling the ignition of and the conduction periods of an ignitron or similar tube type.

For igniting ignitrons, it is' known to use a capacitor which is continually charged and which discharges at every desired ignition in a circuit including, in addition to the igniter of the ignitron and to a switch usually in the form of a thyratron, a non-linear element which is, as a rule, a choke coil.

In order that the invention may be readily carried into effect, it will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing.

A known circuit arrangement of the aforesaid type is shown diagrammatically in FIG. 1. A capacitor 1 is charged by an alternating current source (not shown) through a rectifier 2. The capacitor can discharge via a choke coil 3 and a thyratron 4 through an igniting electrode 5 into cathode 6 of an ignitron 7,'as soon and as often as a voltage pulse is sufficient amplitude delivered by a pulse source 8, shown in block form, is applied to the control grid 9 of thyratron 4.

In this arrangement, the thyratron current I and the ignition current I are equal, as shown in FIG. 1a. Thus, they have the same peak value and the same duration at each passage of current. Since the igniter requires a high peak current for producing the cathode spot, and also a current of long duration for maintaining the cathode spot, this implies that thyratrons of comparatively high power are necessary, and that moreover the passage of current is immediately followed by a high, steeply rising inverse voltage across the thyratron. This latter voltage constitutes a heavy load for the cathode of the thyratron and thus for the most vulnerable part thereof.

An object of the invention is to provide an arrangement in which the said disadvantages are avoided, or at least occur to a greatly reduced extent.

Accordingly, this invention features, inter alia, an ignition circuit arrangement for igniting ignitrons which comprises an output circuit, which via the thyratron switching means couples the ignitron to the capacitor, and is divided into two branches. One branch includes the ignition-path of the ignitron and at least part of the choke coil and is traversed by the igniting current during the discharging period of the capacitor, and the other branch includes a rectifier. The series-combination of the two branches form a closed circuit including the said rectifier, the ignition-path and the choke coil conveying the part of the igniting current which is delivered subsequently by the energy accumulated in the choke coil during the discharging period of the capacitor.

FIGS. 2 to 5 show four difierent embodiments of the invention in which the above-mentioned principle may be carried into efiect, and curves 2a to 5a drawn beside these figures show the associated variation of the igniting current I In the circuit arrangement shown in FIG. 2, the anode of the thyratron 4 is connected directly to the capacitor 1 and two branches emanate from the cathode. hand branch in the figure includes the ignition-path 5, 6

The right- 3,246,203 Patented Apr. 12, 1966 or the ignitron 7 and the choke coil 3 and the left-hand branch includes a rectifier 10 and a resistor 11. The resistor 11 is connected to the left-hand end of the choke coil 3 so that the coil 3, together with the elements 11, 10 and 5, 6 forms a closed circuit. The energy accumulated in the choke coil 3 during the discharging period of capacitor 1 can flow away in this circuit through the ignitionp-ath 5, 6. The igniting current thus varies as illustrated in FIG. 2a, having a steep initial portion and a more gradual declining portion. Comparison of FIGS. 2a and la shows that the duration of the igniting current is considerably longer with equal peak values. If the ignitron is used for welding purposes, as will often be the case, this longer durationof the igniting current increases the likelihoodjthata stable arc will be established between the anode andthe cathode of the ignitron. This is especially important with strongly inductive ignitron circuits or if a large. controlangle is used.

The circuit arrangement shown in FIG. 3 diifers from that of FIG. 2 only in that the choke coil 3 has a tapping which is connected to the zero terminal of capacitor 1. The tapping need not be located at the center of coil 3. The effect thereof is that during the period in which the capacitor 1 discharges, the igniting current traverses only the part of the choke coil which is connected directly to the cathode 6 of ignitron 7 and thus encounters a lower resistance from the coil than does the subsequent portion of the igniting current in the circuit 3, 1t), 5, 6 which has to traverse the whole of the coil 3. The igniting current I in the circuit of FIG. 3 varies as shown in FIG. 3a. From FIGS. la and 3a, in which the thyratron current I is shown in broken lines, it may be seen that this current has a peak value equal to that of the igniting current, but is of a much shorter duration, namely 20 microseconds only as compared with 350 to 500 microseconds for the igniting current.

The circuit arrangement shown in FIG. 4 is intended to be used if the cathode of the ignitron is connected to the phase lead of the AC. supply voltage instead of to the neutral lead of the supply. The high voltage is then kept away from the parts 1, 2 and 4, by means of a transformer 12 which is insulated for high voltage. The first part of the igniting current passes through the right-hand winding of transformer 12 and that branch of the igniting circuit which includes the igniter 5, 6' and the choke coil 3. Because of the absence of the blocking action of the thyratron, this branch also includes a rectifier 13. The subsequent part of the igniting current passes through the rectifier 16 in series with the elements 13, 5-6 and 3, from the aforesaid branch. FIG. 4a shows the variation of the voltage V. across the capacitor, and the variation of the thyratron current I and the igniting current 1 as in FIG. 2a.

The circuit arrangement shown in FIG. 5 utilizes an autotransformer 14 having a tap which is connected to the igniting electrode 5 of ignitron 7 through the choke coil 3. The end of which remote from thyratron 4 is connected to the cathode 6 through a rectifier 15. Another branch leads from the cathode 6 to the cathode of the thyratron through a second rectifier 16 poled in the same pass direction as rectifier 15.

In this circuit arrangement, due to the action of the autotransformer 14, not only the duration but also the peak value of the thyratron current I, are considerably smaller than those of the igniting current 1 as may be seen from FIG. 5a.

What is claimed is:

1. A circuit for igniting an ignitron having an anode, an ignition electrode and a cathode which form an ignition path, said circuit comprising a capacitor, means for supplying unidirectional current to said capacitor thereby to store an electrical charge thereon, a discharge circuit for said capacitor comprising a control device having a control electrode and first and second electrodes for establishing a unidirectional current path, an ignition circuit comprising first and second parallel connected branches, said first branch comprising a'first portion of an inductor continues .tomaintain said current flow in said predeterin series with the ignition'path of said ignitron, said secnd branch comprising a rectifier element in series with a V I second portion of said inductor, said first and second branches together forming a closed unidirectional circuit with said ignitron, ignition'path'and which includes both portions of said inductor, circuit. means connected to a point on said inductor for completing the discharge circuit of said capacitor, means coupled to said control electrode for periodically rendering said'control device conductive thereby to discharge said capacitor through said discharge circuit, and means for interconnecting said discharge circuit with said ignition circuit whereby in response to the discharge of said capacitor a current -flow is initiated in said, inductor element and between said ignition'eleetrode 'and'said cathode in a direction so as to ignite said ignitron, said rectifier element being poled so that following the discharge of said capacitor the energy stored in said inductor element continues to maintain said current flow in said direction to ignite said ignitron. I a

2. Apparatus as described in claim 1 wherein said control device. comprises a thyratron having an anode connected to one terminal of said capacitor and a cathode connected to said ignition electrode and to one electrode of said rectifier element, and said circuit means being further connected to the other terminal of said capacitor.

3. A circuit for igniting an ignitron having an ignition electrode, a cathode and an anode, said circuit comprising a, capacitor, means for supplying a unidirectional current to saidcapacitorthereby tostore an electrical charge thereon, a discharge circuit for said capacitor comprising a control device having a control electrode and first and second electrodes for establishing a unidirectional current path, an autotransformer having first and second winding ele-'. ments, means for connecting said first winding element in said discharge circuit in series with saidlcurren-t path of saidcontrol device, an ignition circuit comprising an inductance element, a rectifier elementand said autotransformer second winding element serially, connected between said ignition electrode and said cathode to form a closed series circuit, said ignition circuit further comprising another branch comprising a secondrectifier element connected in parallel with the series combination of said first rectifier element and said autotr-ansformer, said first and second rectifier elements being poled in the same direction, means coupled to said control {electrode for periodia cally rendering said control device conductive thereby to discharge said capacitor through said discharge circuit,

and means for interconnecting said discharge circuit with said ignition circuit thereby to. initiate current flow in said mined direction.

4. Apparatus asv described in claim 3 wherein said control device comprises a thyratron having an anode connected to one terminal of said capacitor and a cathode connected to the cathode of said second rectifier element and to one terminal of said autotransformer first winding element, and means connecting the anodes of said first and second rectifier elements together and to the other terminal of saidcapacitor.

5. A circuit for igniting an ignitron having an ignition electrode, a cathode and an anode, said circuit comprising a capacitor, means for supplying a unidirectional current to said capacitor thereby to store an electrical charge thereon, a discharge circuit for said capacitor comprising a thyratron control device having a control electrode and an anode and a cathode for establishing a unidirectional current path, and means including said control device for interconnecting said capacitor and said ignitron ignition and cathode electrodes, said interconnecting means further comprising a transformer having a primary and a secondary winding, means connecting said thyratron anode to one terminal of said capacitor and means connectingsaid thyratron cathode to one terminal of said primary winding, means for connecting the other terminal of said primary winding to the other terminal of said capacitor, an inductance element serially connected in said dischargecircuit between said control device and said ignition and cathode electrodes, an ignition circuit comprising said inductance element and a rectifier element serially connectedbetween said ignition electrode and said cathode to form a closed series circuit, said rectifier element comprising first and second serially connected diodes poled in the same direction, means, for connecting said secondary winding acrossone of said diodes, and means coupled to said control electrode for periodically rendering said thyratron conductive thereby to discharge ,said capacitor through said discharge circuit whereby a current, flow is initiated in said inductanceelement and between said ignition electrode and said cathode in a direction so as to ignite'said ignit'ron, said rectifier element being poled so that following the discharge of said capacitor the energy stored in said inductance element continues to maintain said current flow in said direction to ignite said ignitron.

References Cited by the Examiner UNITED STATES PATENTS 2,295,635 9/1942 Collom 315 27'3 XR 2,730,659 1/1956 Hess 315--263 X-R 2,955,233 10/1960 Paleyet a1; 315-273 XR FOREIGN PATENTS 1,063,721 8/1959 Germany.

JOHN W. HUCKERT, PrimaryExaminer.

JAMESD, KALLAM, GEORGE N. WESTBY,

ARTHUR GAUSS, Examiners. 

1. A CIRCUIT FOR IGNITING AN IGNITRON HAVING AN ANODE, AN IGNITION ELECTRODE AND A CATHODE WHICH FROM AN IGNITION PATH, SAID CIRCUIT COMPRISING A CAPACITOR, MEANS FOR SUPPLYING UNIDIRECTIONAL CURRENT TO SAID CAPACITOR THEREBY TO STORE AN ELECTRICAL CHARGE THEREON, A DISCHARGE CIRCUIT FOR SAID AN CAPACITOR COMPRISING A CONTROL DEVICE HAVING A CONTROL ELECTRODE AND FIRST AND SECOND ELECTRODES FOR ESTABLISHING A UNIDIRECTIONAL CURRENT PATH, AN IGNITION CIRCUIT COMPRISING FIRST AND SECOND PARALLEL CONNECTED BRANCHES, SAID FIRST BRANCH COMPRISING A FIRST PORTION OF AN INDUCTOR IN SERIES WITH THE IGNITION PATH OF SAID IGNITRON, SAID SECOND BRANCH COMPRISING A RECTIFIER ELEMENT IN SERIES WITH A SECOND PORTION OF SAID INDUCTOR, SAID FIRST AND SECOND BRANCHES TOGETHER FORMING A CLOSED UNIDIRECTIONAL CIRCUIT WITH SAID IGNITRON IGNITION PATH AND WHICH INCLUDES BOTH PORTIONS OF SAID INDUCTOR, CIRCUIT MEANS CONNECTED TO A POINT ON SAID INDUCTOR FOR COMPLETING THE DISCHARGE CIRCUIT OF SAID CAPACITOR, MEANS COUPLED TO SAID CONTROL ELECTRODE FOR PERIODICALLY RENDERING SAID CONTROL DEVICE CONDUCTIVE THEREBY TO DISCHARGE SAID CAPACITOR THROUGH SAID DISCHARGE CIRCUIT, AND MEANS FOR INTERCONNECTING SAID DISCHARGE CIRCUIT WITH SAID IGNITION CIRCUIT WHEREBY IN RESPONSE TO THE DISCHARGE OF SAID CAPACITOR A CURRENT FLOW IS INITIATED IN SAID INDUCTOR ELEMENT AND BETWEEN SAID IGNITION ELECTRODE AND SAID CATHODE IN A DIRECTION SO AS TO IGNITE SAID IGNITRON, SAID RECTIFIER ELEMENT BEING POLED SO THAT FOLLOWING THE DISCHARGE OF SAID CAPACITOR THE ENERGY STORED IN SAID INDUCTOR ELEMENT CONTINUES TO MAINTAIN SAID CURRENT FLOW IN SAID DIRECTION TO IGNITE SAID IGNITRON. 